The invention relates to an optoelectronic module having a laser diode configured on a substrate. The laser diode can be driven using an electronic drive device. In this case, at least one electrode of the laser diode is connected to the substrate or is coupled to the substrate. That is to say, one electrode is arranged on the substrate itself or is coupled to the substrate via an electric line.
Given high data rates in the gigahertz range, an important role is assumed by the aspect of the high-frequency link between the laser diode and the assigned electronic drive system. In particular, edge-emitting laser diodes are distinguished mostly by a small internal impedance in the order of magnitude of 1-10 ohms. In contrast, the integrated circuits for driving the laser diode mostly have the technically customary output impedance of approximately 50 ohms. The supply leads are also correspondingly designed for a line impedance of 50 ohms.
Moreover, the link between the high-frequency signals and ground potential plays an important role. Frequently, the ground potential of the high-frequency signal referenced to the substrate is connected to the ground potential of the housing via a comparatively long electrically conducting connection, or this connection is completely absent.
Both the differences in impedance between the electronic drive system and the laser diode, and the poor or missing link between the high-frequency signals and the ground potential work out as mismatching. Consequently, the high-frequency signals generated in the electronic drive system are retroreflected to a considerable degree, in particular by the laser diode, and are therefore not available for the electrooptic modulation of the laser diode. This can lead to a substantial worsening of the signal integrity and/or worsen the reflected components of the high-frequency signal, and the electromagnetic compatibility (EMC) of the optoelectronic module with surrounding electronic components.
It is known from the prior art to increase the output power of the electronic drive system in the event of mismatching between the electronic drive system and the laser diode in such a way that an adequate modulation of the laser diode is achieved despite the partial reflection of the high-frequency drive signal. The EMC problems have to be solved in such cases by expensive shielding measures.
It is accordingly an object of the invention to provide an optoelectronic module and an optoelectronic transceiver, which overcome the above-mentioned disadvantages of the prior art apparatus of this general type in a simple and cost-effective way.
With the foregoing and other objects in view there is provided, in accordance with the invention, an optoelectronic module including: a substrate; and a laser diode for being driven using an electronic drive device. The laser diode is configured on the substrate. The laser diode has an impedance and at least one electrode connected or coupled to the substrate. The substrate has specific electrical conduction properties. For matching the impedance of the laser diode to the electronic drive device, the substrate is designed as an electric line coupled to the electrode of the laser diode, and the impedance of the laser diode is matched by setting the specific electrical conduction properties of the substrate.
In accordance with an added feature of the invention, the substrate includes a semiconductor material.
In accordance with an additional feature of the invention, an electric contact is provided for applying a defined electric potential to the substrate. The electric contact is configured on the substrate at a spacing from the electrode. The substrate has a conduction region between the electrode of the laser diode and the electric contact of the substrate. The specific electrical conduction properties of the substrate are properties in the conduction region. During operation of the laser diode, the specific electrical conduction properties of the substrate match the impedance of the laser diode to that of the electronic drive device.
In accordance with another feature of the invention, the substrate has a resistivity; and the substrate has a semiconductor material with a doping determining the resistivity of the substrate.
In accordance with a further feature of the invention, the substrate has an electrically insulating section in the conduction region; the substrate has a capacitive reactance in the conduction region; and the electrically insulating section has dimensions influencing the capacitive reactance in the conduction region.
In accordance with a further added feature of the invention, the substrate has a first surface and a second surface; the electrode and the laser diode are configured on the first surface; and the electric contact is configured on the second surface of the substrate.
In accordance with a further additional feature of the invention, the substrate has a planar design; and the first surface of the substrate is configured opposite the second surface of the substrate.
In accordance with yet an added feature of the invention, the electrically insulating section is formed as an electrically insulating layer on at least one surface selected from a group consisting of the first surface and the second surface.
In accordance with yet an additional feature of the invention, the electrically insulating layer is an SiO2 layer.
In accordance with yet another feature of the invention, the electrically insulating section is formed as an electrically insulating layer on the first surface.
In accordance with yet a further feature of the invention, the electrode of the laser diode is configured on the electrically insulating layer.
In accordance with another added feature of the invention, the substrate has a first surface and a second surface; the electrode and the laser diode are configured on the first surface; and the electric contact is configured on the second surface of the substrate.
With the foregoing and other objects in view there is also provided, in accordance with the invention, an optoelectronic transceiver that includes the an optoelectronic module.
In order to inventively match the impedance of the laser diode to the assigned electronic drive device, the substrate is designed as an electric line coupled to one electrode of the laser diode, and the impedance is matched by setting the specific electric conduction properties of the substrate.
In this way, in addition to the mechanical function as carrier of the laser diode and the thermal function of dissipating the heat produced in the laser diode, the substrate additionally fulfills an electric function of impedance matching between the laser diode and the assigned electronic drive system. This ensures a better utilization of the electric drive signal of the electronic drive system by the laser diode. Furthermore, the optoelectronic module has improved EMC properties.
The inventive solution utilizes the fact that the substrate can be designed with specific electrical conduction properties, that is to say defined ohmic, capacitive and/or inductive impedance components, in such a way that the total impedance of laser diode and the substrate is matched to the impedance of the electronic drive system.
The inventive solution is simple and cost effective, since for impedance matching, an already present and required component, specifically the carrier substrate of the laser diode, is used. Additional functions are provided thereby in conjunction with the same number of parts.
It is preferred for a defined electric potential to be applied to the substrate via an electric contact that is arranged on the substrate at a spacing from one electrode. As previously described, in a conduction region of the substrate material that extends between one electrode of the laser diode and the electric contact, the substrate has specific electrical conduction properties that serve during the operation of the laser diode to match the impedance to the assigned electronic drive device.
It is advantageous when the substrate has a semiconductor material. In particular, using a doped semiconductor material permits the ohmic resistivity of the substrate to be set accurately via the selection of different dopants and dopant concentrations.
The substrate is preferably designed with an electrically insulating section in the conduction region. As a result, the capacitive reactance component of the substrate in the conduction region can be influenced in a simple way by the dimensions of the electrically insulating section.
On the substrate, one electrode of the laser diode is preferably arranged on a first surface of the substrate, and the electric contact of the substrate is arranged on a second surface of the substrate. By suitably selecting the spacing between one electrode of the laser diode and the electric contact of the substrate, it is possible to set the ohmic resistance of the conduction region together with the parameter of the specific conductance of the substrate in the conduction region.
Given a planar design of the substrate, for example, as a silicon wafer, the first surface and the second surface are assigned to the two opposite side faces of the substrate.
The electrically insulating section is preferably designed as an electrically insulating layer that at least partially forms the first and/or the second surface of the substrate.
In a preferred embodiment, the substrate has an electrically insulating layer on the first surface, and one electrode of the laser diode is arranged on this electrically insulating layer.
Particularly in the case of a silicon substrate, the electrically insulating layer can be designed simply as a thin silicon dioxide layer.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an optoelectronic module, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.